Internal combustion engines having a relatively small number of cylinders provide automobile makers with an attractive solution to the need for improved fuel economy. In order to compensate for reduction of cubic capacity vehicle manufacturers developed technologies to improve engine power, such as direct fuel injection, turbocharging, and variable timing for inlet and exhaust camshafts. In this way six- and eight-cylinder engines can be scaled down without losing available horsepower.
An undesirable consequence of engines with a small number of cylinders is high crankshaft torsional vibration and high engine block vibration caused by forces, such as first and second order forces, that are not cancelled. Such vibrations are ultimately transmitted through the engine mounts and driveline to the vehicle structure.
Engineers managed these vibrations to one extent or another through a variety of approaches, many of which increase the cost of construction and reduce fuel economy. One accepted solution to overcome excessive vibration is the provision of one or more pendulums on the crankshaft to lower the torsional vibration of the crankshaft and the consequent driveline vibration. Such crankshaft-mounted pendulums function as vibration absorbers as they are tuned to address and thus cancel out vibrations generated by crankshaft rotation, thus smoothing torque output of the crankshafts. This approach is taken as well by designers of some airplane piston engines where the pendulums smooth output torque and reduce rigid body motion.
An example of a pendulum vibration absorber associated with an engine crankshaft is set forth in U.S. Pat. No. 4,739,679, assigned to the assignee of the instant application. According to the arrangement set forth in this patent, the pendulum is bolted to the crankshaft so that the shoulder bolts carry the load in sheer along the shoulder. However, the pendulum of this design is intended for an I-4 engine that does not require counterweights for balancing insofar as an I-4 is balanced in first order. Accordingly, so long as the pendulums are symmetric, the I-4 will still be balanced.
Such is not the case for the I-3 engine. In this engine, pendulums are necessary as counterweights for balance since the I-3 engine has a first order pitching moment. To obtain the necessary balance without adding the large inertia of U.S. Pat. No. 4,739,679, the pendulums must be designed in a similar shape as a conventional counterweight.
However, attachment to the crankshaft has been calculated to result in bolt failure at high speed due to sheer. The prototype method of attaching a pendulum crankshaft is not feasible in production. One method conceived was to bolt on the pendulums along the sides. This method is not feasible since the clamp load is not sufficient to prevent the pendulum from moving radially. The clamp load interface would slip and bolts would fail in sheer.
Thus a new approach to the attachment of the pendulum to the crankshaft in smaller engines is needed to address the problems associated with known arrangements and to reduce the amount of torsional vibration produced by the internal combustion engine.